Field of the Invention
The invention relates to a disconnecting device for direct current interruption between a direct current source and an electrical apparatus, comprising a current-conducting mechanical switch and a power electronics unit connected thereto, and an energy store, which is charged by an arcing voltage generated on the switch by an arc as the switch is being disconnected. In this case, a direct current source is understood to be a photovoltaic generator (PV generator, solar system), and an electrical apparatus is, in particular, an inverter.
Description of the Background Art
From DE 20 2008 010 312 U1, a photovoltaic system (PV system) or a solar system with a so-called photovoltaic generator is known, which in turn has solar modules which are combined into groups of partial generators, which in turn are connected in series or are present in parallel strings, wherein the direct current power of the photovoltaic generator is fed into an alternating voltage network via an inverter. Since as a result of the system, a PV system continuously provides, on the one hand, an operating current and an operating voltage in the range between 180V (DC) and 1500V (DC), and since on the other hand, for example for installation, assembly or service purposes or in particular for general personal protection, reliable separation of the electrical components or devices from the photovoltaic system acting as a direct current source is desired, a corresponding disconnecting device must be capable of performing an interruption under load, i.e. without previously switching off the direct current source.
For load separation, a mechanical switch (switching contact) can be used with the advantage that a galvanic separation of the electrical apparatus (inverter) from the direct current source (photovoltaic system) is produced when the contact has been interrupted. If, on the other hand, power semiconductor switches are used for load separation, unavoidable power losses occur in the semiconductors even during normal operation. In addition, no galvanic separation and therefore no reliable personal protection is ensured with such power semiconductors.
DE 102 25 259 B3 discloses a plug connector designed as a load breaker which, in the manner of a hybrid switch, comprises a semiconductor switching element in the form of, for example, a thyristor in the housing of the inverter, and main and auxiliary contacts which are connected to photovoltaic modules. The main contact leading in an unplugging operation is connected in parallel with the trailing auxiliary contact, which is connected in series with the semiconductor switching element. In this case, the semiconductor switching element is controlled for purposes of arc prevention or arc suppression by periodically switching it on and off.
A hybrid electromagnetic direct current switch with an electromagnetically actuated main contact and an IGBT (insulated gate bipolar transistor) can also be provided as a semiconductor switch for direct current interruption (DE 103 15 982 A2). However, such a hybrid switch has an external energy source for operating a power electronics unit with a semiconductor switch.
WO 2010/108565 A1, which corresponds to U.S. Pat. No. 8,742,828, discloses a hybrid disconnecting switch with a mechanical switch or disconnecting element, and a semiconductor electronics which is connected in parallel therewith and which essentially comprises at least one semiconductor switch, preferably an IGBT. The semiconductor electronics does not have an additional energy source and, with the mechanical switch closed, is current-blocking, that is to say virtually current-free and voltage-free. The semiconductor electronics gains the energy required for its operation from the disconnecting device, that is, from the breaker system itself, for which purpose the energy of the arc arising when the mechanical switch is opened is used. In this case, the semiconductor electronics is connected to the mechanical switch on the trigger side in such a way that the arcing voltage switches the semiconducting electronics in a conducting manner via its switching contacts as a result of the arc.
As soon as the semiconductor electronics is switched to conduct current, the arc current starts to commutate from the mechanical switch to the semiconductor electronics. The corresponding arcing voltage or the arc current in this case charges an energy store in the form of a capacitor, which discharges specifically to produce arc-free switching-off of the semiconductor electronics, whilst generating a control voltage. The predetermined time duration or time constant and thus the charging duration of the energy store or capacitor determines the duration of the arc. Following the charging process, a timing element starts, during which the semiconductor electronics is controlled arc-free and current-blocking. The time duration of the timer is set to a secure deletion.